The present invention relates to charge injection device (CID) image sensors and, more particularly, to a novel integrated CID image sensor having an on-chip voltage preamplifier for each row of sensing array cells.
It is well known that the sensitivity of a charge-injection-device (CID) sensor is limited by the signal-to-noise ratio of the device signals. Improved sensitivity, allowing wider dynamic range and concomitant operation in lower incident light levels, requires that the temporal noise level be significantly reduced. The temporal noise in a CID image sensor is typically determined by the Johnson noise of both the row select multiplexer and the video amplifier, and by the capacitance associated with the signal sense line. Present CID image sensors incorporate a current sensing scheme which tends to peak the resulting noise current at a relatively high frequency. Because row selection is accomplished by multiplexing, wherein a multiplexer connects a different one of the row lines to the input of the single video amplifier, the capacitance attributable to the signal line is relatively large. Thus, it would be highly beneficial to reduce the capacitance and/or noise attributes associated with the peripheral selection circuitry, for selecting that one cell of a CID sensing array to provide an output at any particular instant, to reduce the temporal noise level and thus provide increased sensitivity and dynamic range.